SEARCH · Searcharxiv

Results for “physics.ao-ph”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

arXiv2014

Daily pollution forecast using optimal meteorological data at synoptic and local scales

We present a simple framework to easily pre-select the most essential data for accurately forecasting the concentration of the pollutant PM$_{10}$, based on pollutants observations for the years 2002 until 2006 in the metropolitan region of Lisbon, Portugal. Starting from a broad panoply of different data sets collected at several meteorological stations, we apply a forward stepwise regression procedure that enables us not only to identify the most important variables for forecasting the pollutant but also to rank them in order of importance. We argue the importance of this variable ranking, showing that the ranking is very sensitive to the urban spot where measurements are taken. Having this pre-selection, we then present the potential of linear and non-linear neural network models when applied to the concentration of pollutant PM$_{10}$. Similarly to previous studies for other pollutants, our validation results show that non-linear models in average perform as well or worse as linear models for PM$_{10}$. Finally, we also address the influence of Circulation Weather Types, characterizing synoptic scale circulation patterns and the concentration of pollutants.

physics.ao-ph↗

arXiv2017

Invariant Radiative Cooling and Mean Precipitation Change

We show that radiative cooling profiles, when described in temperature coordinates, are insensitive to surface temperature $T_s$. We argue this theoretically as well as confirm it in cloud-resolving simulations of radiative convective equilibrium (RCE). This $T_s$-invariance holds for shortwave and longwave cooling separately, as well as their sum. Furthermore, the $T_s$-invariance of radiative cooling profiles leads to a simple expression for the $T_s$-dependence of column-integrated cooling and hence precipitation, and gives insight into why mean precipitation increases at a rate of $2 -3\%\ \mathrm{K^{-1}}$ in RCE. The relevance of these results to global climate simulations is assessed, and the $T_s$-invariance is found to hold in the mid and upper troposphere. In the lower troposphere, the pressure-invariance of cloud layers and circulation tends to dominate.

physics.ao-ph↗

arXiv2018

New High Performance GPGPU Code Transformation Framework Applied to Large Production Weather Prediction Code

We introduce "Hybrid Fortran", a new approach that allows a high performance GPGPU port for structured grid Fortran codes. This technique only requires minimal changes for a CPU targeted codebase, which is a significant advancement in terms of productivity. It has been successfully applied to both dynamical core and physical processes of ASUCA, a Japanese mesoscale weather prediction model with more than 150k lines of code. By means of a minimal weather application that resembles ASUCA's code structure, Hybrid Fortran is compared to both a performance model as well as today's commonly used method, OpenACC. As a result, the Hybrid Fortran implementation is shown to deliver the same or better performance than OpenACC and its performance agrees with the model both on CPU and GPU. In a full scale production run, using an ASUCA grid with 1581 x 1301 x 58 cells and real world weather data in 2km resolution, 24 NVIDIA Tesla P100 running the Hybrid Fortran based GPU port are shown to replace more than 50 18-core Intel Xeon Broadwell E5-2695 v4 running the reference implementation - an achievement comparable to more invasive GPGPU rewrites of other weather models.

cs.DC↗

arXiv2018

A Data-driven Approach to Detecting Precipitation from Meteorological Sensor Data

Precipitation is dependent on a myriad of atmospheric conditions. In this paper, we study how certain atmospheric parameters impact the occurrence of rainfall. We propose a data-driven, machine-learning based methodology to detect precipitation using various meteorological sensor data. Our approach achieves a true detection rate of 87.4% and a moderately low false alarm rate of 32.2%.

physics.ao-ph↗

arXiv2018

Systematic Study of Weather Variables for Rainfall Detection

Numerous weather parameters affect the occurrence and amount of rainfall. Therefore, it is important to study these parameters and their interdependency. In this paper, different weather and time-related variables -- relative humidity, solar radiation, temperature, dew point, day-of-year, and time-of-day are analyzed systematically using Principal Component Analysis (PCA). We found that four principal components explain a cumulative variance of 85%. The first two principal components are applied to distinguish rain and no-rain scenarios as well. We conclude that all 7 variables have similar contribution towards rainfall detection.

physics.ao-ph↗

arXiv2018

A Potential Low Cost Remote Sensing Using GPS Derived PWV

In this paper, the Precipitable Water Vapor (PWV) content of the atmosphere is derived using the Global Positioning System (GPS) signal delays. The PWV values from GPS are calculated at different elevation cut-off angles. It was found that the significant range of elevation cut-off angles is from 5 degrees to 50 degrees. The PWV values calculated from GPS using varying cut-off angles from this range were then compared to the PWV values calculated using the radiosonde data. The correlation coefficient and the Root Mean Square (RMS) error between the GPS and radiosonde derived PWV decreases with the increasing cut-off angle and the distance between the two. The seasonal parameters also effect the relation between the two.

physics.ao-ph↗

arXiv2018

Stability of boundary layer flow based on energy gradient theory

The flow of the laminar boundary layer on a flat plate is studied with simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

physics.flu-dyn↗

arXiv2018

Detecting fog where satellite systems are limited

Surface level hydrometeors, and specifically fog, cause attenuation of the signal level measured by microwave communication networks. These networks operate at frequencies of tens of GHz and form the data transport infrastructure between cellular base stations. Thus, wireless communication links are, effectively, an existing fog monitoring facility. Operational costs are minimal, since the network is already deployed in the field, and measurements are already stored by many of the cellular providers for quality assurance purposes. This study shows the potential of microwave communication networks for the detection of fog in challenging conditions where satellite systems are often limited. In a first event, the ability to detect fog using commercial microwave links, at a time when the satellite cannot detect the phenomena due to high level cloud cover obscuring the ground level fog, is demonstrated. The ability of the microwave system to rule out ground level fog at times when the satellite detects a low-lying stratus cloud, but cannot identify whether it is adjacent to the ground or at higher elevations above it, is demonstrated in a second event. The results indicate the operative potential of this technique to assist end users in reliable decision making that have highly important economic and safety implications.

physics.ao-ph↗

arXiv2018

APE dissipation is a form of Joule heating. It is irreversible, not reversible

Available Potential Energy (APE) dissipation plays a central role in the description of mixing in turbulent stratified fluids. The dominant paradigm is that it converts APE into background gravitational potential energy ${\rm GPE}_r$, and that the APE thus converted can be infinitely recycled back into APE by external buoyancy fluxes such as high-latitude cooling in the oceans. In this paper, we argue that such a paradigm is unphysical, because its corollary is that APE dissipation is neither truly dissipative nor irreversible, while also violating energy conservation in more subtle ways. In this paper, we prove from first principles that in reality, APE dissipation is a form of Joule heating, which --- like viscous dissipation --- can only increase ${\rm GPE}_r$ via locally expanding the fluid parcels, a tiny effect. ${\rm GPE}_r$ thus primarily increases at the expense of the exergy of the stratification, a subcomponent of the background internal energy, regardless of whether the flow is laminar or turbulent. The results greatly clarify the energetics of mechanically- and buoyancy-driven circulations. As a side benefit, our results yield a new physical principle justifying why turbulent mixing tends to homogenise the fluid's materially conserved variables rather than relax the fluid towards thermodynamic equilibrium.

physics.ao-ph↗

arXiv2018

Simple geometric approximations for global atmospheres on moderately oblate planets

Certain geometric approximations such as the widely used traditional shallow-atmosphere, spherical-geoid (TSA-SG) and the deep-atmosphere, spherical-geoid (DA-SG) approximations boil down to the specification of a spatial metric tensor. In order to eliminate the leading-order errors due to the SG and TSA approximations, a sequence of three metric geometric approximations of increasing accuracy at high altitudes is obtained. Their metric tensors possess a simple, closed-form analytical expression. The approximations capture to leading order the oblateness of the planet, the widening of atmospheric columns with height, the horizontal and vertical variations of gravity and the non-traditional part of the Coriolis force. Furthermore, for the first two approximations, the horizontal metric is conformal (proportional) to the spherical metric, which simplifies analytical and numerical formulations of the equations of motion.

physics.ao-ph↗

arXiv2018

A High-Resolution Future Wave Climate Projection for the Coastal Northwestern Atlantic

A high-resolution wave climate projection for the northwestern Atlantic Ocean has been conducted to help assess possible regional impacts due to global climate change. The spectral wave model NOAA WAVEWATCH III is utilized with three coupled (two-way) grids to resolve the northwestern Atlantic and coastal southern and eastern USA at approximately 21 km and 7 km respectively, and covers the periods 1979--2003 (historic) and 2075--2099 (future). Hourly wind field forcings are provided by a high-resolution AGCM (MRI-AGCM 3.2S; 21 km) and allow for better modeling of large storm events (important for extreme event statistics). Climatological (25-year) comparisons between future and historical periods indicate significant wave heights will decrease in the northwestern Atlantic Ocean (-5.7 %) and Gulf of Mexico (-4.7 %) but increase in the Caribbean Sea (2.4 %). Comparisons also indicate that large changes in mean wave direction will occur in the Gulf of Mexico (5.0°), with the largest occurring west of the Florida peninsula (over 15°).

physics.ao-ph↗

arXiv2018

The Solar Wind and Climate: Evaluating the Influence of the Solar Wind on Temperature and Teleconnection Patterns Using Correlation Maps

Evaluating the magnitude of natural climate variations is important because it can greatly affect future climate policies. As an example, we examine the influence of changes in solar activity (solar wind in particular) on surface temperatures (Ts) and major teleconnection patterns such as the Arctic Oscillation and Pacific Decadal Oscillation. We compared correlation maps (spatial distribution of correlation coefficient) for a combination of Ts and a geomagnetic index (aa, an indicator of solar wind strength) and a combination of Ts and the teleconnection patterns. The phase of the quasi-biennial oscillation of the equatorial zonal wind and magnitude of sunspot number were considered. As a result, we found that the influence of the solar wind is as strong as that of the teleconnection patterns and hence, the former appears to affect the climate via the latter. It was also found that both the solar wind and ultraviolet change should be considered to explain the influence of solar activity variability, i.e., a multi-pathway scheme is necessary.

physics.ao-ph↗

arXiv2018

Optical Depth and Vertical Profile of Stratospheric Aerosol based on Multi-Year Polarization Measurements of the Twilight Sky

The method of detection of light scattering on stratospheric aerosol particles on the twilight sky background is considered. It is based on the data on sky intensity and polarization in the solar vertical at zenith distances of up to 50 deg from the sunset till the moment of the Sun depression to 8 deg below the horizon. The measurements conducted in central Russia since 2011 had shown the negative trend of stratospheric aerosol content, this can be related with the relaxation of the stratosphere after the number of volcanic eruptions during the first decade of XXI century.

physics.ao-ph↗

arXiv2018

On the Warming of the Southern Hemisphere since 1955 and Recent Slowing-Down: Role of Sea Ice, Sun Spot and El Nino Variability

The importance of the sea ice retreat in the polar regions for the global warming and the role of ice-albedo feedback was recognized by various authors [1,2]. Similar to a recent study of the phenomenon in the Arctic [3] we present a semi-quantitative estimate of the mechanism for the Southern Hemisphere (SH). Using a simple model, we estimate the contribution of ice-albedo feedback to the mean temperature increase in the SH to be 0.5 +/- 0.1 K in the years 1955 to 2015, while from the simultaneous growth of the greenhouse gases (GHG) we derive a direct warming of only 0.2 +/- 0.05 K in the same period. These numbers are in nice accordance with the reported mean temperature rise of 0.75 +/- 0.1 K of the SH in 2015 since 1955 (and relative to 1880). Our data also confirm previously noticed correlations between the annual fluctuations of solar intensity and El Nino observations on the one hand and the annual variability of the SH surface temperature on the other hand. Our calculations indicate a slowing down of the temperature increase during the past few years that is likely to persist. Assuming a continuation of the present trends for the southern sea ice and GHG concentration we predict the further temperature rise to decrease by 33 % in 2015 to 2025 as compared to the previous decade.

physics.geo-ph↗

arXiv2018

Solar Irradiance Forecasting Using Triple Exponential Smoothing

Owing to the growing concern of global warming and over-dependence on fossil fuels, there has been a huge interest in last years in the deployment of Photovoltaic (PV) systems for generating electricity. The output power of a PV array greatly depends, among other parameters, on solar irradiation. However, solar irradiation has an intermittent nature and suffers from rapid fluctuations. This creates challenges when integrating PV systems in the electricity grid and calls for accurate forecasting methods of solar irradiance. In this paper, we propose a triple exponential-smoothing based forecasting methodology for intra-hour forecasting of the solar irradiance at future lead times. We use time-series data of measured solar irradiance, together with clear-sky solar irradiance, to forecast solar irradiance up-to a period of 20 minutes. The numerical evaluation is performed using 1 year of weather data, collected by a PV outdoor test facility on the roof of an office building in Utrecht University, Utrecht, The Netherlands. We benchmark our proposed approach with two other common forecasting approaches: persistence forecasting and average forecasting. Results show that the TES method has a better forecasting performance as it can capture the rapid fluctuations of solar irradiance with a fair degree of accuracy.

stat.AP↗

arXiv2018

Hard bremsstrahlung from a high-voltage atmospheric discharge and its anisotropy

The results of the experiments on recording hard gamma radiation and measurements of its angular distribution at the initial stage of a laboratory high-voltage atmospheric discharge are presented. The experiments were performed on an ERG installation at a voltage of $\sim 1$ MV, an atmospheric discharge current of up to 12 kA, and a gap of 0.55 m. The duration of the voltage pulse was about 1~$μ$s with a pulse rise time of 150-200 ns. The radiation was recorded by an assembly of 10 identical scintillation detectors installed each 10$^\circ$ around the circumference of a quarter of a circle with a curvature of 1 m. In order to separate the radiation with energies from 20 keV to 1.5 MeV, Al and Pb filters of different thicknesses were used. The obtained results show that, as a rule, a multi-beam radiation pattern and several bursts of radiation (each with a directional pattern) are recorded in each shot. In a considerable number of "shots", hard radiation with photon energies comparable to or exceeding the maximum electron energy corresponding to the applied voltage is recorded. In these cases, a needle-like radiation pattern is observed, including at large angles to the axis of the discharge. This may indicate the acceleration of electrons in different plasma channels.

physics.plasm-ph↗

arXiv2018

Mesoscale circulation in the Alaskan Stream area

The Alaskan Stream is the northern boundary current in the subarctic North Pacific. This area is characterized by significant temperature, salinity and density differences between coastal and open-ocean waters and strong mesoscale dynamics. In this paper we demonstrate the transport pathways of Alaskan Stream water in the eastern subarctic Pacific and the eastern Bering Sea from October 1, 1994 to September 12, 2016 with the help of altimetry-based Lagrangian maps. A mesoscale eddy activity along the shelf-deep basin boundaries in the Alaskan Stream region and the eastern Bering Sea is shown to be related with the wind stress curl in the northern North Pacific in winter. A significant correlation is found between the concentration of chlorophyll a in the Alaskan Stream area and eastern Bering Sea in August - September and the wind stress curl in the northern North Pacific in November - March. The mesoscale dynamics, forced by the wind stress curl in winter, may determine not only lower-trophic-level organism biomass but also salmon abundance/catch in the study area.

physics.ao-ph↗

arXiv2021

Accurately Quantifying Radiative Cooling Potentials: A Temperature-correction to the Transmittance-based approximation

Theoretical calculations of the cooling potential of radiative cooling materials are crucial for determining their cooling capability under different meteorological conditions and evaluating their performance. To enable these calculations, accurate models of long-wave infrared downwelling atmospheric irradiance are needed, However, the transmittance-based cosine approximation, which is widely used to determine radiative cooling potentials, does not account for the cooling potential arising from heat loss to the colder reaches of the atmosphere itself. Here, we show that use of the approximation can lead to > 10% underestimation of the cooling potential relative to MODTRAN 6 outputs. We propose a temperature correction to the transmittance-based approximation which accounts for heat loss to the cold upper atmosphere, and significantly reduces this underestimation, while retaining the advantages of the original model. In light of the widespread and continued use of the transmittance-based model, our results highlight an important source of potential errors and a means to correct for them.

physics.ao-ph↗